In modern high speed printing machines, e.g. laser printers, the individual papers of the successive documents or jobs are printed in successive order of their page number and outputted with their printed side down. The printed papers are stacked in a stacker. The sheets of the individual documents are then in correct order. If the sheets are printed in Duplex mode, the odd page numbers usually face down. The printing may also be done in the reverse order of the sheet numbers and the stacking performed with the printed side or the odd page numbers up.
In U.S. Pat. No. 5,439,209 to Kurt Runzi a stacker is disclosed which is capable of separating the individual jobs on the stack. The papers are fed to a conveyor belt which transports them to the stack in a cassette. A lateral guide rail for the papers can be swiveled between two positions. The switching position of the guide rail is changed each time a document or job is finished, i.e. after the last page of that job has passed the conveyor belt.